1. Field of the Invention
The present invention relates to navigation devices, and more particularly to a signal pick-off arrangement for detecting the alignments of a magnetic needle.
2. Description of the Prior Art
Electronic compasses have had great revivals in recent popularity, particularly since the advant of inexpensive digital displays. While elegant in their displays such electronic compasses utilize the earth's magnetic field as the reference and are therefore not much more accurate than a good magnetic compass. Thus an electronic or a magnetic compass are both inherently of lower accuracy, an accuracy acceptable for the lay person in his ordinary endeavors of navigating a small boat or some other vehicle. In the most basic form, a magnetic compass includes the use of a magnetized needle typically suspended on a pin for minimal friction losses, where the needle seeks alignment with the local earth magnetic flux. This needle then travels above the surface of a dial which is inscribed with the necessary markings for determining the alignment thereof relative the axis of the vehicle. In order to isolate the roll and pitch motions of the vehicle from the plane of the needle, quite often gimballed arrangements are utilized comprising a roll and pitch gimbal axis and a bob weight. In this form a relatively inexpensive instrument is now commonly available which because of the number produced is now realizable to a relatively high accuracy at minimal cost.
An electronic compass utilizes what is known as the Hall effect where semiconductor devices are fixed to a hard platform referenced to the vehicle. This Hall effect semiconductor then sends the local earth magnetic field to produce the sine and cosine components thereof for readout. In exemplary electronic compass of such type is that disclosed in U.S. Pat. No. 4,030,204. In each instance where flux sensors are utilized, the earth's magnetic flux is directly sensed with a consequently large error because of the weakness thereof. Thus electronic compasses of the foregoing kind, while more rugged and less mechanically complex, are also less accurate. A magnetic needle when properly damped by fluid is still one of the more accurate sensing devices and when properly constructed and installed is still the most prevalent device publicly used.